This application is based on Application No. 2000-255520 filed in Japan on Aug. 25, 2000, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a liquid crystal control device for exposing light onto a photosensitive member or performing an indication as a display device using a liquid crystal for example, by driving and controlling the liquid crystal.
2. Description of the Related Art
FIG. 15 is a perspective view illustrating the construction of a print head for a conventional liquid crystal drive unit disclosed in Japanese Patent Application Laid-Open No. No. 7-256928 for example.
In FIG. 15, white light from a halogen point light source 100 is separated into red, green and blue light by means of a color liquid crystal shutter 101, and continuously irradiated to an end face of an acrylic rod 102 in a time shifted manner.
Here, note that the acrylic rod 102 is covered with a reflection foil, on which aluminum, etc., is deposited except for a light emitting face thereof, and it has a function of converting incident light entered from an end thereof into linear or line-shaped light to be radiated downward.
Thus, red, green and blue linear light is continuously irradiated to a monochrome shutter array 103 in a time shifted manner.
Within the monochrome shutter array 103, there are three rows of pixels, corresponding to red, green and blue, respectively, which are driven to permit only the light of the colors specified respectively.
For instance, when linear red light in the shape of a line is irradiated, only pixel rows corresponding to red can be passed or penetrated and the other two pixel rows are kept in a blocking state.
Accordingly, the respective linear red, green and blue lights modulated by the monochrome shutter array 103 are focused on a photosensitive paper 105 by means of a SELFOC lens array 104 (i.e., tradesman of a converging lens array).
At this time, the respective red, green and blue linear lights are sequentially exposed to the photosensitive paper 105 at the same place thereof through a relative movement of the photosensitive paper 105 to the monochrome liquid crystal shutter array 103, so that a two-dimensional print image can be obtained.
With the conventional print head for a liquid crystal drive unit, photosensitive paper is exposed in the above manner to form a gradation or halftone image thereon.
In order to speed up the printing, for two above-mentioned kinds of liquid crystal shutters (i.e., the liquid crystal shutter 101 and the monochrome shutter array 103), there have generally been employed STN (super twisted nematic) type liquid crystal, ferroelectric liquid crystal, etc., which can respond at high speed in the unit of milliseconds by applying thereto an AC voltage of ten kHz or so.
On the other hand, the display with a liquid crystal shutter is called an LCD (Liquid Crystal Display). This is constructed such that a liquid crystal is inserted between two glass substrates in the form of an upper and a lower glass substrate with a distance therebetween of about 5 xcexcm, and a spacer is disposed between the upper and lower glass substrates so as to prevent them from coming in contact with each other. In addition, a polarizing plate is generally set up on each of the upper and lower glass substrates in such a manner that the direction of vibration of one of the polarizing plate is at right angles with respect to that of the other. The Liquid crystal has a property that upon application of an electric field thereto, the arrangement of molecules therein is varied according to the electric field. Therefore, for example, the liquid crystal can be controlled in such a manner that it allows light to penetrate therethrough upon application of a voltage, but intercept or block light when there is no voltage supplied to them. In addition, colors of half tones can be expressed by changing the penetration of light through the strength of the voltage applied.
As a method for driving the liquid crystal, first striped transparent electrodes are installed on the upper glass substrate in the direction of X, and second striped transparent electrodes are installed on the lower glass substrate in the direction of Y. According to a matrix driving technique as one example, a voltage is imposed to the points of intersection where a selected electrode in the X direction intersect with a selected electrode in the Y direction, to thereby control the amount of light penetrating through the liquid crystal. According to an active matrix driving technique as another example, a transistor is disposed at each of the intersections between the electrodes in the X direction and the electrodes in the Y direction, with electric current being accumulated in the transistors lying at those portions which form pixels.
Moreover, display techniques used for a display include a penetration type and a reflection type display technique. According to the penetration type display technique, back lights are disposed under the liquid crystal so that the light emitted from the back lights penetrates through the liquid crystal to thereby provide a display or indication. On the other hand, according to the reflecting type display technique, a reflection plate is placed under the liquid crystal with which light is reflected at the bottom or lower side thereof so as to give a display.
With the conventional liquid crystal control device as described above, two operational modes including a light-penetrating or transparent mode and a light-blocking mode are alternatively changed from one to the other to form a gradation or gray-scale image by utilizing the specific property of the liquid crystal in which upon application of a voltage, molecules of the liquid crystal are caused to change their arrangement along the direction of an electric field generated. However, there arise the following problems. That is, in the case of a positive type liquid crystal, immediately after the liquid crystal has changed from the light-blocking mode to the light-penetrating or transparent mode, there would develop a condition in which the liquid crystal is not stabilized due to a backflow (i.e., spring phenomenon), so no uniform exposure or display could not be obtained. Accordingly, in cases where exposure is carried out to a photosensitive member, the exposure becomes unstable and hence any high quality picture record cannot be achieved, with the result that it is difficult to provide a uniform display with a display device.
The present invention is intended to obviate the above-mentioned problems and has for its object to provide a liquid crystal control device which is capable of obtaining a uniform exposure or a uniform display.
According to one aspect of the present invention, there is provided a liquid crystal control device comprising: a light source controller for controlling the turning on and off of a light source; a liquid crystal driving section for driving a liquid crystal; and a control unit for delaying a timing, at which the light source is turned on by the light source controller, with respect to a timing, at which the liquid crystal is driven to operate by the liquid crystal driving section.
According to another aspect of the present invention, there is provided a liquid crystal control device comprising: a light source controller for controlling the turning on and off of a light source; a liquid crystal driving section for driving a liquid crystal; and a control unit for delaying a timing, at which the light source is turned off by the light source controller, with respect to a timing, at which the liquid crystal is driven to operate by the liquid crystal driving section.
In a preferred form of the invention, the control unit adjusts the timing, at which the light source is turned on by the light source controller, according to a temperature characteristic of the liquid crystal.
According to a further aspect of the present invention, there is provided a liquid crystal control device comprising: a light source controller for controlling the turning on and off of a light source; a liquid crystal driving section for driving a liquid crystal; and a control unit for controlling a timing, at which the light source is turned on by the light source controller, and a timing, at which the liquid crystal is driven to operate by the liquid crystal driving section; wherein the light source controller controls the light source in such a manner that a quantity of light emitted by the light source gradually increases when the light source is turned on.
According to a still further aspect of the present invention, there is provided a liquid crystal control device comprising: a light source controller for controlling the turning on and off of a light source; a liquid crystal driving section for driving a liquid crystal; and a control unit for controlling a timing, at which the light source is turned on by the light source controller, and a timing, at which the liquid crystal is driven to operate by the liquid crystal driving section; wherein the light source controller controls the light source in such a manner that the light source emits light in a pulsed manner when turned on.
In another preferred form of the invention, the light source comprises a light emitting type element.
In a further preferred form of the invention, the thickness of a liquid crystal layer of the liquid crystal is 3.0 xcexcm or less.
In a still further preferred form of the invention, the liquid crystal comprises a positive type TN liquid crystal.